Shell and tube heat exchangers4 (8)

The shell and tube heat exchanger, also known as the jacketed heat exchanger, is a type of inter-tube heat exchanger where the walls of the tube bundle enclosed in the shell serve as the heat transfer surface. This type of heat exchanger is characterized by its simple construction, low cost, wide flow cross-section, and ease of scale cleaning; however, it has a low heat transfer coefficient and occupies a large space. It can be made from various materials (primarily metal) and is used under high temperature and pressure conditions, making it the most common type.

Tubular heat exchangers include several types: stationary tube bundles of steam-water heat exchangers, tubular steam-water heat exchangers with compensators, floating-head steam-water heat exchangers, U-shaped tube bundles of steam-water heat exchangers, tubular steam-water heat exchangers with corrugated sections, sectional water-water heat exchangers, and others. The main control parameters of tubular heat exchangers are heating area, hot water flow rate, heat transfer, heat carrier parameters, and others.

The shell-and-tube heat exchanger consists of a shell, a bundle of heat exchange tubes, a tube sheet, baffles, and a tube box. The shell is usually cylindrical, with a bundle of tubes installed inside, whose ends are fixed on the tube sheet. The two heat exchange flows, the cold and the hot, move in opposite directions: one inside the tubes, called the tube side flow, and the other outside the tubes, called the shell side flow. To increase the heat transfer coefficient of the shell side flow, several baffles are typically installed in the shell. The baffles increase the velocity of the shell side flow, causing it to repeatedly cross the bundle of tubes along a specific trajectory, enhancing the flow turbulence. The heat exchange tubes on the tube sheet can be arranged in an equilateral triangle or square pattern. The equilateral triangle arrangement provides a more compact layout, higher turbulence in the shell side flow, and a greater heat transfer coefficient; the square arrangement is convenient for cleaning the shell side space and is suitable for flows prone to fouling.

The main control parameters of the shell-and-tube heat exchanger are heating area, hot water flow rate, heat transfer, and heat carrier parameters.

Each passage of fluid through the tube space is called a tube pass; each passage through the shell is called a shell pass. The figure shows the simplest heat exchanger with one shell pass and one tube pass, which is briefly referred to as a 1-1 heat exchanger. To increase the fluid velocity in the tubes, baffles can be installed in the tube boxes at both ends, dividing all tubes into several groups. Thus, the fluid passes through only part of the tubes during each pass, making multiple passes through the tube space, which is called multiple tube passes. Similarly, to increase the fluid velocity in the shell space, longitudinal baffles can be installed in the shell, forcing the fluid to pass through the shell space multiple times, which is called multiple shell passes. Multiple tube and shell passes can be used together.

In a tubular heat exchanger, due to the temperature difference between the fluids inside and outside the tubes, the temperature of the shell and the tube bundle also differs. If the temperature difference is significant, large thermal stresses arise in the heat exchanger, leading to bending, rupture, or detachment of the tubes from the tube sheet. Therefore, when the temperature difference between the tube bundle and the shell exceeds 50°C, appropriate compensation measures must be taken to eliminate or reduce thermal stresses. Depending on the compensation measures used, tubular heat exchangers can be divided into the following main types:

In a fixed-tube-sheet heat exchanger, the tube sheets at both ends of the tube bundle are integrated with the shell as a single unit, making the structure simple. However, this design is only suitable for heat exchange operations with a small temperature difference between the hot and cold fluids, where mechanical cleaning in the shell side is not required. When the temperature difference is slightly higher and the pressure in the shell side is not too high, flexible expansion rings can be installed on the shell to reduce thermal stress.

② In a floating-head heat exchanger, the tube sheet at one end of the tube bundle can float freely, completely eliminating thermal stress; additionally, the entire tube bundle can be withdrawn from the shell, facilitating mechanical cleaning and maintenance. Floating-head heat exchangers are widely used, but their design is quite complex and their cost is high.

③ U-shaped heat exchanger. Each heat exchange tube is bent into a U-shape and fixed at both ends in the upper and lower zones of the same tube plane, with the inlet and outlet separated by a partition in the tube box. This type of heat exchanger completely eliminates thermal stress, its structure is simpler than that of the floating head, but the tube space is difficult to clean.

④ Vortex heat exchanger with thermal film The vortex heat exchanger with thermal film utilizes the latest vortex film heat transfer technology, enhancing heat exchange efficiency by altering the fluid's flow state. As the medium passes along the surface of the vortex tube, it thoroughly cleans the pipe surface, thereby increasing heat exchange efficiency. The maximum power can reach 10,000 W/m²℃. Additionally, this design ensures corrosion resistance, thermal resistance, high-pressure resistance, and scale formation prevention. In other types of heat exchangers, fluid channels have fixed flow directions, leading to boundary layer formation on the heat exchange tube surface and reduced convective heat transfer coefficients.

 

Features:

1. Highly efficient and energy-saving, the heat transfer coefficient of this heat exchanger ranges from 6000 to 8000 W/m²·°C.

2. Fully made of stainless steel, long service life, can reach 20 years or more.

3. Converting laminar flow into turbulent flow enhances heat exchange efficiency and reduces thermal resistance.

4. Fast heat exchange, resistance to high temperatures (400°C) and high pressure (2.5 MPa).

5. Compact design, takes up little space, has a lightweight, is easy to install, and saves on construction and installation costs.

6. Flexible structure, full range, high practical orientation, cost savings.

7. Wide range of applications, suitable for significant ranges of pressure, temperature, and heat exchange with various media.

8. Low maintenance costs, easy operation, long descaling cycle, convenient cleaning.

9. The use of nanothermal film technology significantly increases the heat transfer coefficient.

10. Wide range of applications, can be widely used in fields such as thermoelectricity, industry and mining, petrochemicals, centralized urban heating, food and pharmaceutical industries, energy and electronics, machinery manufacturing and light industry.

11. The heat transfer tubes are made of copper pipes with rolled fins on the outer surface, offering high thermal conductivity and a large heat exchange area.

12. The guide plate directs the fluid flow in the inter-tube space of the heat exchanger on straight sections, and the distance between the plates can be adjusted according to the optimal flow velocity. The design is robust and capable of ensuring heat exchange for fluid flows with large or even extremely large capacity and high pulsation frequency in the inter-tube space.

13. When the medium in the annular space is oil, it is applicable for heat exchange with low-viscosity and relatively clean oils.